The present invention relates to a plasma etching apparatus and, more particularly, to a microwave plasma etching apparatus which is suitable for rapid etching of Si, SiO.sub.2, W, Al, etc.
Improvement in mass-productivity of plasma etching apparatus is strongly required at present. To meet this requirement it is desired that an increase in number of wafers which can be processed at one time, and a reduction of time needed for etching a single wafer, that is, faster etching be achieved. The first above, method, is currently in use in batch process plasma etching, while the other is currently in use in single wafer process plasma etching. In batch processing many wafers are etched at one time; hence, this method is ideal for mass production. In the single wafer processing each wafer is etched separately. This technique requires imporvement for mass production.
FIGS. 1 to 3 show schematic diagram of such conventional etching apparatus. Both FIGS. 1 and 2 show batch process apparatus. FIG. 1 is a microwave plasma etching apparatus; and FIG. 2 is an RF (Radio Frequency) plasma etching apparatus. In both apparatuses, a plurality of wafers 6 placed on a plate 7 or an electrode 10 are etched simultaneously. FIG. 3 shows a single wafer process plasma etching apparatus, and this apparatus is substantially similar to that shown in FIG. 2. Its difference from FIG. 2 is that a slab of material is put on the electrode 10 and the wafers are etched one by one.
Improvement for mass production is required in both single and batch wafer processing. However, in practice, most manufacturers try to etch faster; in the single wafer process because:
(1) Although 3 inch diameter wafer is mainly used at present, wafers of 4-6 inch diameter will be used in the future. To simultaneously process many large wafers in batch processing, the etching chamber 9 has to be made larger. This requires that the floor area or the height of the apparatus be increased, but this is not in accord with the current trend toward miniaturization of plasma etching apparatus.
(2) As semiconductor circuit elements become smaller, more accurate etching is required. The current state of the art is such that irregularities appear on the surface of the wafer prior to etching. It is diffucult to etch such wafers simultaneously.
The microwave plasma etching apparatus of FIG. 1 uses plasma which is generated by the combined effects of a microwave at 2.45 GHz generated by a magnetron 1 and a magnetic field produced by solenoids 3 and a permanent magnet 8. This kind of etching allows submicron pattern delineation with damage and contamination, but the etch rate is lower compared with the RF plasma etching method. It is obvious that there is a need to increase the etch rate for single wafer microwave plasma etching apparatus.